The long range goals of the proposed research are to elucidate the molecular mechanisms by which agonists linked to phosphoinositide metabolism alter contractility of the mammalian heart. A key hypothesis to be tested is that alpha-adrenergic, Kappa-opioid and endothelin-1 receptors are coupled to pathways in which specific diacylglycerols become elevated, leading to selective activation of protein kinase C isoforms and phosphorylation of specific proteins associated with the contractile apparatus. The effects of phosphorylation on rates of activation and relaxation, as well as on the kinetics of product release steps during the cross-bridge cycle will be examined using the novel method of pulse photolysis of caged compounds to rapidly alter Ca2+, inorganic phosphate and ADP in single cardiac myocytes. Information obtained will provide a basis for understanding changes in cardiac performance during heart failure, ischemic/reperfusion injury or during chronic diseased states such as hypertension or diabetes.